Mobile terminals, besides a telephone functionality, accommodate more and more different wireless applications, such as WLAN (Wireless Local Access Network), GPS (Global Positioning System), Bluetooth and possibly mobile television. Low noise amplifiers (LNAs) are often used for each of these applications to improve system sensitivity performance.
Due to an increasing number of antennas it is a big challenge for system designers to place antennas in mobile terminals so as to keep the mobile terminals small and, at the same time, to avoid crosstalk among the different applications. To reduce this crosstalk or coupling between the various applications, a LNA can be placed directly behind a respective antenna to yield a so-called active antenna, such that the impact of the environment and the degradation of performance due to PCB (Printed Circuit Board) line loss can be eliminated. This kind of topology, for example, can often be found in notebooks and flip phones in which the antenna and the LNA are placed behind an LCD (Liquid Crystal Display).
Typically, a LNA does not only comprise input and output terminals for RF signal lines but also two or even three additional terminals for DC power supply and on/off control lines, which are connected to a receiver IC on the main PCB.